MAX6970 查看數據表（PDF） - Maxim Integrated

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MAX6970

8-Port, 36V Constant-Current LED Driver

Maxim Integrated 

8-Port, 36V Constant-Current LED Driver

Pin Description

PIN

1

2

3

4

5–12

13

14

15

16

EP

(TSSOP)

NAME

FUNCTION

GND

DIN

CLK

Ground

Serial-Data Input. Data is loaded into the internal 8-bit shift register on CLK’s rising edge.

Serial-Clock Input. Data is loaded into the internal 8-bit shift register on CLK’s rising edge.

LE

Load-Enable Input. Data is loaded transparently from the internal shift register to the output latch while

LE is high. Data is latched into the output latch on LE’s falling edge and retained while LE is low.

OUT0–OUT7 LED Driver Outputs. OUT0 to OUT7 are open-drain, constant-current-sinking outputs rated to 36V.

OE

Output-Enable Input. High forces outputs OUT0 to OUT7 high impedance without altering the contents

of the output latches. Low enables outputs OUT0 to OUT7 to follow the state of the output latches.

DOUT Serial-Data Output. Data is clocked out of the 8-bit internal shift-register to DOUT on CLK’s rising edge.

SET

LED Current Setting. Connect SET to GND through a resistor (RSET) to set the maximum LED current.

V+

Positive Supply Voltage. Bypass V+ to GND with a 0.1µF ceramic capacitor.

—

Exposed Pad. Although not required, connecting EP to ground improves thermal performance.

Detailed Description

The MAX6970 LED driver comprises a 4-wire serial inter-

face driving eight constant-current-sinking, open-drain

output ports. The outputs drive LEDs in either static or

multiplex applications (Figure 1). The constant-current out-

puts are guaranteed for current accuracy, not only with

chip-supply voltage variations (5V ±10% and 3V to 5.5V),

but also over a realistic range of driver output voltage drop

(0.8V to 2.5V). The drivers use current-sensing feedback

circuitry (not simple current mirrors) to ensure very small-

current variations over the full allowed range of output volt-

age (see the Typical Operating Characteristics).

The 4-wire serial interface comprises an 8-bit shift reg-

ister and an 8-bit transparent latch. The shift register is

written through a clock input, CLK, and a data input,

DIN, and the data propagates to a data output, DOUT.

The data output allows multiple drivers to be cascaded

and operated together. The contents of the 8-bit shift

register are loaded into the transparent latch through a

latch-enable input, LE. The latch is transparent to the

shift register outputs when high, and latches the current

state on the falling edge of LE.

Each driver output is an open-drain, constant-current

sink, which should be connected to the cathode of either

a single LED or a series string of multiple LEDs. The LED

anode can be connected to a supply voltage of up to

36V, independent of the MAX6970 supply, V+. The con-

stant-current capability is up to 55mA per output, set for

all eight outputs by an external resistor, RSET.

4-Wire Serial Interface

The serial interface on the MAX6970 is a 4-wire serial

interface, using four inputs (DIN, CLK, LE, OE) and a

data output (DOUT). This interface is used to write dis-

play data to the MAX6970. The serial-interface data

word length is 8 bits, D0–D7. See Figures 2 and 3.

The functions of the five interface pins are as follows.

DIN is the serial-data input, and must be stable when it

is sampled on the rising edge of CLK. Data is shifted in,

MSB first. This means that data bit D7 is clocked in first,

followed by 7 more data bits, finishing with the LSB D0.

CLK is the serial-clock input, which shifts data at DIN into

the MAX6970’s 8-bit shift register on its rising edge.

LE is the load input latch that transfers data from the

MAX6970 8-bit shift register to its 8-bit latch when LE is

high (transparent latch), and latches the data on the

falling edge of LE (Figure 2).

The fourth input provides output-enable control of the

output drivers. OE is high to force outputs OUT0 to

OUT7 high impedance without altering the contents of

the output latches, and low to enable outputs OUT0 to

OUT7 to follow the state of the output latches.

OE is independent of the serial-interface operation.

Data can be shifted into the serial-interface shift regis-

ter and latched regardless of the state of OE.

DOUT is the serial-data output, which shifts data out

from the MAX6970’s 8-bit shift register on the rising

edge of CLK. Data at DIN is propagated through the

shift register and appears at DOUT eight clock cycles

later. See Figure 2.

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